A cataract is a condition where the crystalline lens of an eye becomes cloudy or opaque enough to reduce vision. Cataract surgery today is a systematic process whereby an eye surgeon will disassemble the cataractous lens and remove and replace it with a synthetic prosthetic lens. Typically, the vision is restored without the need for thick spectacle correction.
The normal, natural, crystalline lens lies behind the iris of the eye and separates the anterior and posterior segments of the eye. The anterior chamber is normally filled with fluid called the aqueous humor. The cornea serves as the anterior boundary of the anterior chamber of the eye. The lens fills a thin membranous capsule that is supported radially by very fine hairlike fibers called zonules which in turn are supported by a smooth circular band of muscle called the cilliary body. The relaxation or contractile action of the cilliary body is thought to cause the expansion and contraction of the lens responsible for the natural lens's ability to dynamically alter its focal length during accommodation.
While early cataract surgeries involved removal of both the lens and its surrounding capsule, the current state of the art involves leaving most of the capsule intact so that the remaining capsule can support a synthetic prosthetic lens. In order to remove the lens from the capsule, an opening, or capsulotomy, must be made in the capsule. A capsulorhexis is an opening in the capsule having a particular smooth shape and particularly suitable for both removing the natural lens from the capsule and allowing insertion of a prosthetic lens into the residual capsule.
Most surgeons would argue that, outside of disassembling and removing the natural lens itself, the creation of a good capsulorhexis is probably the most important step in cataract surgery. The first step in performing a capsulorhexis entails puncturing the anterior capsule of the lens with a sharp needle like instrument or cystotome, creating an initial tear and a small capsular flap pedicle. Next, the flap of the initial tear is grasped with fine micro forceps. The surgeon then directs the tips of forceps to shear the anterior capsule in a clockwise or counterclockwise fashion thereby creating a quasi-circular opening in the anterior capsule of the lens. The current method requires the surgeon to grasp the edge of the capsular flap multiple times before completion. Depending on the anatomy of the patient's eye, this can take up to 5 or 10 minutes to complete. The aperture created in the anterior capsule is more often than not, imprecise in its diameter and irregular in its quasi-circular contour. Complications associated with this technique include poor control of capsulorhexis diameter, inadvertent propagation of capsular tear to the peripheral capsule and increased operative time.